Are ride-sharing services such as Lyft, SideCar and Tickengo casual services for drivers to give rides to strangers or are they more like full-time occupations akin to taxis for regular drivers to generate an income?

That's a key question as the California Public Utilities Commission looks at regulating these services. In October, the CPUC issued cease-and-desist letters to ride-sharing startups SideCar; Lyft, which is owned by Zimride; and Tickengo; then later fined SideCar, Lyft and Uber $20,000 each. (Tickengo, after meeting with the CPUC and dropping its "instant ride" feature, had its cease-and-desist dropped.)

The CPUC, which is now preparing to have hearings to examine the issue, argues that the startups, like airport vans and limousines, are "charter-party carriers" that are subject to CPUC licensing and regulation.

Tickengo in October announced the hiring of noted former San Francisco mayor Willie Brown as its lawyer and advisor. Brown has recently filed an argument to the CPUC that unsurprisingly supports Tickengo. If implemented, his proposals could force other startups in the space to make changes. Brown argues that Tickengo is not a charter-party carrier but is just connecting drivers with people looking for rides. He also argues that Tickengo is similar to 511.org, the government-run ride-sharing service to match drivers and riders. The reason: Tickengo limits the amount of revenue drivers can make to the the average annual cost of car ownership or $8,776 according to the AAA.

Brown says in the filing: "Pure ridesharing platforms not operating as charter-party carriers but simply enabling licensed drivers and riders to connect and share empty seats in their cars, such as Tickengo and the government-run 511.org, must be defined clearly by the CPUC in order to avoid competitive misunderstandings from passenger carriers and taxis and improve the lives of Californians."

Brown also makes the case that according to CPUC code, the CPUC does not regulate "passenger vehicles carrying passengers on a noncommercial basis." The question is, what is "noncommerical"? To clarify this, Brown proposes implementing a cap on revenue for drivers in ridesharing programs as Tickengo does. Essentially if you drive on one of these services and make less than the cost of ownership, you are in the eyes of the law just picking people up in the course of your everyday driving to pay for your gas and other car expenses--and not making a profit. The maximum revenue, Brown suggests, should be the average annual cost of vehicle ownership -- currently $8,776, according to the AAA. Because it's difficult to calculate the exact cost of each ride, taking the AAA number as an average is the best cap, Brown argues.

This $8,776 number, or about $731 per month, would certainly be less than many drivers on other ride sharing services make, at least according to those drivers I have spoken to. Many drivers make $100 or more per day driving on these services, so getting above $8,776 per year is not difficult without a cap. Anyone who drives at least eight days a month, at least on an annual basis, would be over the cap and be illegal under Brown's proposal.

Others in this space such as Lyft and SideCar have argued that they should not be regulated by the CPUC because they do not own cars or hire drivers and are instead technology platforms that connect the drivers and riders.